Struct Tape 

pub struct Tape { /* private fields */ }

A reverse-mode autodiff tape: the recorded operation graph plus the forward value of each node.

Build an expression by calling the operation methods, which append nodes and return Var handles; the forward value is computed eagerly as each node is pushed. Call grad on an output node to run the reverse pass and accumulate the partial derivatives with respect to every input.

Examples

use sim_lib_numbers_ad::Tape;

// f(a, b) = a * b + a, at a = 2, b = 5.
let mut tape = Tape::new();
let a = tape.input(0, 2.0);
let b = tape.input(1, 5.0);
let product = tape.mul(a, b);
let out = tape.add(product, a);
assert_eq!(tape.value(out), 12.0);
// df/da = b + 1 = 6, df/db = a = 2.
assert_eq!(tape.grad(out, 2), vec![6.0, 2.0]);

Implementations

impl Tape

pub fn new() -> Self

Creates an empty tape.

pub fn constant(&mut self, value: f64) -> Var

Records a constant node and returns its handle.

pub fn input(&mut self, slot: usize, value: f64) -> Var

Records an independent input bound to gradient slot slot with the given value, and returns its handle.

pub fn add(&mut self, a: Var, b: Var) -> Var

Records a + b and returns the handle of the sum.

pub fn sub(&mut self, a: Var, b: Var) -> Var

Records a - b and returns the handle of the difference.

pub fn mul(&mut self, a: Var, b: Var) -> Var

Records a * b and returns the handle of the product.

pub fn div(&mut self, a: Var, b: Var) -> Var

Records a / b and returns the handle of the quotient.

pub fn sin(&mut self, arg: Var) -> Var

Records sin(arg) and returns its handle.

pub fn cos(&mut self, arg: Var) -> Var

Records cos(arg) and returns its handle.

pub fn exp(&mut self, arg: Var) -> Var

Records exp(arg) and returns its handle.

pub fn ln(&mut self, arg: Var) -> Var

Records ln(arg) and returns its handle.

pub fn sqrt(&mut self, arg: Var) -> Var

Records sqrt(arg) and returns its handle.

pub fn recip(&mut self, arg: Var) -> Var

Records 1 / arg and returns its handle.

pub fn value(&self, var: Var) -> f64

Returns the forward value recorded for var.

pub fn grad(&self, out: Var, n_inputs: usize) -> Vec<f64>

Runs the reverse pass from output out and returns the gradient with respect to the n_inputs input slots.

Seeds the adjoint of out with 1.0, walks the recorded nodes in reverse, and accumulates each input slot’s partial derivative; the returned vector has length n_inputs.

Trait Implementations

impl Clone for Tape

fn clone(&self) -> Tape

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Tape

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Tape

fn default() -> Tape

Returns the “default value” for a type.